The scanning probe microscopy (SPM) is a technique where a measurement probe scans a measurement sample to be examined and, in doing so for example, records a topography of the measurement sample. In this context, a relative movement takes place between the measurement probe and the measurement sample which is attained in such a way that at least the measurement probe or at least the measurement sample is moved. Normally, the relative movement is performed as a lateral movement. In addition, a relative movement can also take place in the vertical direction. One form of the scanning probe microscopy is the scanning force microscopy (SFM). With an atomic force microscope used in this case, the measurement probe is formed in the design of a cantilever which carries a fine measurement tip.
It is a great advantage to combine the scanning probe microscopy with the classic optical microscopy in order to be able to assign more advantageously the measurement results found in the scanning probe microscopy to structures of the measurement sample which, on their part, are taken from optical images of the optical microscopy. In this case and in accordance with the state of the art, an optical image is recorded with the assistance of the optical microscopy and stored preferentially in a digital manner. In a similar way, an SPM-image is produced and stored in the framework of the scanning probe microscopy of the same measurement sample. The images produced in both measurements are finally brought to congruence by means of an image processing program. Certain prerequisites must be fulfilled for this purpose.
First of all, the optical image and the SPM-image must be very accurately calibrated. For the SPM-image, this requirement is already materialised in many commercially available devices because of the use of sensors which detect the lateral movement of the measurement probe. Where the optical image is concerned, an exact calibration is normally waived, particularly in the life sciences. However, a calibration is also possible by means of a lens micrometer for example.
Furthermore, the information from the optical image and the SPM-image must be comparable. This is often the case, however not inevitable, because the mechanisms of the contrast origination are very different in both measurements. In this way, the intended congruence between both images can be impossible.
In addition the SPM-image must show a section, on which sufficient characteristic details are recognisable which are also to be identified in the optical image in order to enable, in this way, an assignment between the two images. This requirement is a major restriction because the SPM-images produced in the scanning probe measurements frequently show only a small section of the measurement sample to be examined. Larger areas of the measurement sample to be examined can frequently not be detected without damaging the measurement probe in the process. In some experimental examinations an SPM-image is not produced because a force-distance-curve is measured only at a single or at several single locations on the measurement sample.
On the whole, the method as described above for the assignment between two image points in the optical image obtained by means of an optical recording device and in the measurement results of the scanning probe microscopy is inexact and has only a limited expressive statement.
It is furthermore known to use a video image recording within the framework of the scanning probe microscopy as an orientation support for the positioning of the measurement probe relative to the measurement sample, where said video recording image shows an optical image of a measurement section of the surface of the measurement sample with the measurement probe positioned thereon. However, problems arise here to that extent that the measurement probe normally shadows off a partial sector of the video image, through which an orientation for the positioning of the measurement probe is made very difficult. In addition, estimating the borders of the video image is just difficult in this way.